As is known, systems for harvesting energy (also known as “energy scavenging systems”) from intermittent environmental energy sources (i.e., ones that supply energy in an irregular way) have aroused and continue to arouse considerable interest in a wide range of fields of technology. Typically, energy harvesting systems are configured to harvest, store and transfer energy generated by mechanical or thermal sources to a generic load of an electrical type.
Low-frequency vibrations, such as, for example, mechanical vibrations of disturbance in systems with moving parts may be a valid source of energy. The mechanical energy is converted, by one or more appropriate transducers (for example, piezoelectric or electromagnetic devices) into electrical energy, which may be used for supplying an electrical load. In this way, the electrical load does not require batteries or other supply systems that are cumbersome and present a low resistance in regard to mechanical stresses.
FIG. 1 is a schematic illustration in the form of functional blocks of an energy harvesting system of a known type.
The energy harvesting system 1 of FIG. 1 comprises: a transducer 2, for example of an electromagnetic or piezoelectric type, subject in use to environmental mechanical vibrations and configured to convert mechanical energy into electrical energy, typically into AC (alternating current) voltages; a scavenging interface 4, for example comprising a diode-bridge rectifier circuit (also known as Graetz bridge), configured to receive at input the AC signal generated by the transducer 2 and supplying at output a DC (direct current) signal for charging a capacitor 5 connected to the output of the rectifier circuit 4; and a DC-DC converter 6, connected to the capacitor 5 for receiving at input the electrical energy stored by the capacitor 5 and supplying it to an electrical load 8. Thus, the capacitor 5 has the function of element for storing energy, which is made available, when required, to the electrical load 8 for operation of the latter.
The transducer 2 is, for example, an electrochemical transducer, or an electromechanical transducer, or an electroacoustic transducer, or an electromagnetic transducer, or a photoelectric transducer, or an electrostatic transducer, or a thermoelectric transducer.
The main disadvantage of the configuration according to FIG. 1 regards the fact that the maximum voltage supplied at output by the scavenging interface 4 is limited by the input dynamics of the DC-DC converter 8.
In applications in which the transducer 2 converts mechanical energy into electrical energy in a discontinuous way and/or the power PLOAD required by the electrical load 8 varies significantly in time, also the voltage VOUT consequently has an evolution variable in time. This causes, for example, a variation of the efficiency factor of the DC-DC converter 6, which is inversely proportional to the value assumed by VOUT. The maximum value of VOUT is further limited by the range of input voltages accepted by the DC-DC converter.
European Patent reference No. EP 2518878 (incorporated by reference) describes a DC-DC converter with a high efficiency factor even in conditions of light load and wide dynamic range of the input voltage. According to this reference, it is important to monitor the inductor current to prevent it from assuming negative values (i.e., to prevent energy from being absorbed by the electrical load). For this purpose, according to the reference, a current-detection circuit is provided, which constantly monitors the inductor current and uncouples the electrical load from the inductor when the current monitored assumes the zero value. A solution of this type requires, in the design step, an accurate trade-off between the desired accuracy of the measurement supplied by the current-detection circuit and the consumption of current of said current-detection circuit.
It is consequently desirable to have available a DC-DC converter that will enable management, in an efficient and, at the same time, accurate way, of supply of the electrical load connected thereto, preventing the DC-DC converter from absorbing energy from the load itself. It is likewise desirable for the management of supply of the load to be carried out automatically and with low current consumption.